Injectable fastener system and method

ABSTRACT

Methods and devices are shown for forming polymer fasteners into bone by expelling the polymer from a cannula. Devices and methods shown allow a user to form multiple fasteners of various sizes without re-loading a device. Devices and methods shown further provide temperature profiles during fastener formation that reduce or eliminate thermal necrosis. Devices and methods shown further provide fasteners with increased strength.

RELATED APPLICATION

This patent application claims the priority benefit of U.S. ProvisionalPatent Application Ser. No. 60/870,757 filed Dec. 19, 2006 and entitled“INJECTABLE FASTENER SYSTEM”, which application is incorporated hereinby reference.

BACKGROUND

The present invention relates to methods for attaching plates to bone.Specific examples include attaching bioresorbable plates to bone usingbioresorbable fasteners.

One current methods for attaching bioresorbable plates to bone fragmentsis bioresorbable screws inserted with a screwdriver either manually orpowered. In order to insert a screw, a threaded hole must be made intothe bone. Threading or tapping is very technique sensitive and if doneincorrectly the screw will not properly hold the plate to the bone. Inaddition, using a manual screwdriver can cause surgeon fatigue if thecase requires more than a few screws to be inserted. Using a poweredscrewdriver speeds insertion and reduces surgeon fatigue, but can stripscrews or torque off the screw head if not handled properly. Thestrength of standard bioresorbable screws is also in need ofimprovement, particularly for load bearing applications. Methods toimprove the strength of resorbable screws through drawing exist, butrequire additional manufacturing processes and require that each screwis individually machined which is more time consuming than injectionmolding of standard screws. Even with these processes, the shearstrength of a screw is diminished since only the minor root diameter ofthe threads impart the load carrying capacity. A screw that is marketedas 1.5 diameter actually only has the strength of a 1.1 diameter pinsince the threads do not impart strength, but only pull out resistance.

Another method for attaching plates is using tacks or rivets. Insertinga tack is very technique sensitive. If the hole is drilled slightlyoversized, a tack will not have sufficient holding power. Even if thehole is of the proper size, a tack generally does not have the same pullout resistance as screws since no threads are formed into the bone.

Eaves et al in U.S. Pat. No. 6,080,161 describe a cannulated pin that isinserted into a hole, heated and deformed in place. This method obviatesthe need to tap the hole and provides a means to accommodate slightvariations in the diameter of the hole that is drilled. However eachfastener must be individually heated adding additional time to theoperative procedure. Also, the heat required to deform the fastener canadd the risk of thermal necrosis to the surrounding tissue.

A relatively new method of fastener insertion is an ultrasonicallyinserted pin inserted using a sonotrode. This method is relativelysimple, does not require tapping and requires only a minimal amount oftraining. The high temperatures created during insertion may inducethermal necrosis. This risk is especially pronounced at the interface ofthe polymer and the bone since this is where the heat is generatedduring insertion. Also, the molten polymer can be extruded under theplate and away from the hole during insertion since the hole that isdrilled is smaller than the diameter of the fastener. Also, the fastenerwill often melt to the plate making removal of one individual fastenerfrom the plate difficult.

In all of the above listed methods, the instrument must be reloadedafter each fastener is inserted. This can be a time consuming processand the fastener is at times unintentionally disengaged from theinstrument during this handling process. In addition, multiple lengthsand diameters of fasteners must be on hand to complete each case. Thesefasteners are packaged in bulky packages and significant space isrequired to house this inventory.

A need exists for an improved fastener and method that addresses theseand other concerns.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of an example bone support attachment deviceaccording to an embodiment of the invention.

FIG. 2 illustrates a stage in a fastening operation according to anembodiment of the invention.

FIG. 3 illustrates another stage in a fastening operation according toan embodiment of the invention.

FIG. 4 illustrates another stage in a fastening operation according toan embodiment of the invention.

FIG. 5 illustrates an example bone support structure for use accordingto an embodiment of the invention.

FIG. 6 illustrates a number of example bone support structures in placeon a skull according to an embodiment of the invention.

FIG. 7 is a flow diagram of an example method according to an embodimentof the invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown,by way of illustration, specific embodiments in which the invention maybe practiced. In the drawings, like numerals describe substantiallysimilar components throughout the several views. These embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the invention. Other embodiments may be utilized and minordeviations may be made without departing from the scope of the presentinvention.

FIG. 1 shows an example of a bone support attachment device 100. In oneembodiment, an amount of polymer is heated to a temperature to providedesired properties such as a temperature high enough to flow, and lowenough to limit or prevent necrosis of tissue. The flowable polymer isexpelled from an end of the bone support attachment device 100, andhardens in place to form a bone fastener. In one embodiment, the polymerincludes a bioresorbable polymer. Selected details and advantages arediscussed in more detail below.

A body 102 forms the structure of the bone support attachment device100. At one end of the device 100 is located an injection cannula 140. Aplunger 130 is configured to pass through the injection cannula 140 andexpel an amount of polymer from the injection cannula 140. The plunger130 shown in the embodiment of FIG. 1 enters the injection cannula at afirst end 142 of the injection cannula 140, which in turn expels anamount of polymer from a second end 144 of the injection cannula 140.

In one embodiment, the plunger is driven with respect to the cannulausing a motor 104. One example of a plunger driving system includes athreaded member 108 coupled to the motor 104, although the invention isnot so limited. Other examples of plunger driving systems include, butare not limited to manual operation, pneumatic operation, a controlledchemical reaction or explosion.

A battery 106 is illustrated in FIG. 1 to power aspects of the bonesupport attachment device 100, including the motor 104. One example of abattery 106 includes a lithium ion battery. Other battery examplesinclude nicad, alkaline, lead acid and nickel metal hydride. Thebatteries 106 can either be of the disposable or rechargeable type. Inalternate embodiments the power source is an AC to DC power supply thatenergizes the motor via a cable.

A polymer supply inlet 124 is shown coupled to a side of the injectioncannula 140. In operation, when a tip 132 of the plunger 130 travelsfrom the first end 142 toward the second end 144 of the injectioncannula 140, the supply inlet 124 is cut off as the tip 132 passes by.When the tip 132 is returned to the first end 142 of the injectioncannula, the supply inlet 124 is again exposed and available to refillthe injection cannula 140.

In one embodiment, a chamber 120 is included to house a block ofpolymer. In one example the chamber 120 includes a cannula, or othercylindrical chamber, although the invention is not so limited. FIG. 1shows a block of polymer 122 located within the chamber 120. Using achamber, and a supply of polymer 122, multiple fasteners can be formedwithout re-loading the bone support attachment device 100. Additionally,fasteners of varying dimensions can be formed from a single polymersupply. For example a fastener with a larger diameter for additionalstrength, or a fastener with a longer length to accommodate a thickerbone support plate can be formed.

To form multiple fasteners, fasteners of varying dimensions, etc., theplunger 130 is withdrawn into a selected location within the injectioncannula 140. Heated polymer is flowed into the injection cannula 140through the polymer supply inlet 124. In one embodiment a local regionof the chamber 120 near the inlet 124 is heated to a sufficienttemperature to flow the polymer. A mechanical feed system, manual feed,or other system provides pressure to inject the liquid polymer at theinlet 124 into the injection cannula 140.

In one embodiment, a starting position of the tip 132 of the plunger 130is varied to adjust a volume of the injection cannula available forpolymer. The flowing polymer will fill the size hole as will bedescribed in more detail below, while the volume of polymer necessary toform the fastener is selected by moving the starting location of the tip132.

In an alternate embodiment, the volume of material that is transferredinto the injection cannula 140 is controlled by the displacement ofcartridge plunger 126. The displacement of this cartridge can becontrolled by any means, including, but not limited to a variabledisplacement mechanism or motor. The means of adjusting the displacementcan be user controlled either through a knob, lever, or switch.

In certain procedures, few fasteners are utilized and thus a volume ofpolymer that can delivery approximately 5 fasteners may be sufficient.In other cases, such as in a craniosynostosis case, more than 150fasteners may be utilized. In these cases a volume of polymer that coulddeliver 20 or more fasteners would be beneficial to reduce the number oftimes that the cartridge needs to be replaced during the procedure. Thenumber of fasteners that can be delivered from each chamber 120 isdependent on the volume of the final fastener and the volume of polymerwithin the chamber 120.

The diameter of the chamber 120 can be modified to suit the requirementsfor size, heat transfer, the size of fastener desired and the number offasteners per cartridge. In the preferred embodiment, the chamberdiameter is between 2 and 4 mm and is between 30 and 50 mm long todeliver up to approximately 20 fasteners. However, invention is not solimited.

In one embodiment, the polymer 122 is heated within at least a portionof the chamber 120. It is desirable to heat the polymer to a temperaturewhere the polymer flows, but at a temperature that is not so high as tocause necrosis of tissue.

In one example the polymer 122 is substantially non-flowable at roomtemperature or physiological temperatures (i.e. 15-37° C.). The polymer122 or portions of the polymer are heated to a temperature of at leastthe glass transition temperature (T_(g)), where the material is renderedsufficiently flowable to be expelled from the chamber 120. In oneembodiment, the polymer 122 and chamber 120 are coordinated together asa cartridge. In other embodiments, the polymer 122 is refillable byitself, and inserted into a chamber 120 that is part of the bone supportattachment device 100.

For one example bioresorbable polymer, the T_(g) is approximately 55° C.While this describes the minimum temperature required to be render thematerial at least partially flowable, it may be advantageous to increasethe temperature to a temperature up to or even above the melting pointof the polymer to reduce the force required to expel the material fromthe injection cannula 140. In one embodiment this temperature is between130 and 180° C., but temperatures between 50 and 250° C. could beutilized. It is, however, advantageous not to excessively heat thepolymer 122. Excessive heat will degrade the polymer, consume additionalpower from the internal power source, heat the instrument itself andcreate an injected polymer that can cause thermal necrosis.

In certain embodiments, the temperature of the polymer 122 within thechamber 120 may not be homogeneous, but rather incorporate a gradientfrom a higher temperature adjacent to the polymer supply inlet 124 to alower temperature where polymer flow is not necessary. This gradient canbe incorporated to optimize the expulsion force while minimizing theissues associated with excessive heat in the polymer addressed above.Certain embodiments may only actively heat the region adjacent to thepolymer supply inlet 124 to provide this gradient.

The method of producing heat in the preferred embodiment is throughelectrically resistive elements that are powered by the battery orbatteries 106. Materials that these electrically resistive elements canbe manufactured from include, but are not limited to, nickel chromiumwire, conductive plastics, ceramics, quartz, etc. In alternativeembodiments, the methods of producing heat may include, but are notlimited to, induction, radio frequency, vibrational, ultrasonic,microwave, frictional, exothermic chemical reactions and infrared. Thetemperature can either be controlled actively or passively. Any knownmethod of active temperature control could be utilized including sensingthe temperature through a temperature sensor and utilizing this tocontrol the amount of power going to the heater. Resistive heatingelements that have a resistance that increases with increasingtemperature (positive temperature coefficient or PTC) can provide ameans of self regulating their temperature actively without additionalcontrols. In alternate embodiments the temperature is controlledpassively without active regulation.

In one embodiment, the polymer includes a thermoplastic polymer 122. Onexample of a thermoplastic polymer includes a bioresorbable aliphaticpolyester. Aliphatic polyesters that can be used in this device include,but are not limited to, homo- and co-polymers of polylactic acid,polyglycolic acid and polycaprolactone. These polymers have been usedfor a number of years in orthopedic devices and are generally regardedas biocompatible and bioresorbable. In the preferred embodiment thepolymer is substantially non-crystalline, but at least partiallycrystalline polymers could be used. Other biocompatible butnon-resorbable polymers could be used in instances where theresorbability was undesirable. Non-resorbable polymers that could beused include, but are not limited to, acrylic, polycarbonate, PEEK,polypropylene, and polyethylene.

In one embodiment, the thermoplastic polymer 122 is compounded with anagent to increase radiopacity, osteoconductivity, osteoinductivity ordeliver a therapeutic agent. Possible radiopacifiers include, but arenot limited to, barium sulfate, zirconium oxide, titanium oxide,titanium dioxide, calcium, tantillum and iodine. Agents to increaseosteoconductivity include, but are not limited to, hydroxyapatite,calcium phosphate and calcium sulfate. Agents to increaseosteoinductivity include, but are not limited to, bone morphogenicproteins and growth factors. Therapeutic agents include, but are limitedto, antibiotics, antiseptics, analgesics, chemotherapeutics, and painmedications.

As mentioned above, in one embodiment the chamber 120 and polymer 122are coordinated together as a replaceable cartridge. This configurationprovides a disposable delivery vessel for the polymer to obviate theneed to clean the internal mechanisms and chambers of the injectiondevice. One example chamber 120 in a cartridge embodiment is constructedof a heat resistance metal such as stainless steel or aluminum or of aheat resistant, biocompatible polymer such as PEEK, polysulphone, Radel,or polycarbonate.

In selected polymer cartridge embodiments, the cartridge furtherincludes a cartridge plunger 126 that expels the polymer when advanced.In one embodiment the cartridge plunger 126 is integral to the polymercartridge and is disposed of along with the polymer cartridge. Inalternative embodiments, the cartridge plunger 126 is a part of the bonesupport attachment device 100 and separated by a seal from the polymer122. The advancement of the cartridge plunger 126 is controlled by thebone support attachment device 100 as described in more detail below.

In an alternate embodiment the polymer 122 is provided in discretesections that are not heated in the chamber 120. The volume of eachsection would correspond to the desired volume of each fastener. In thisembodiment the unheated sections are individually transferred to theinjection cannula through a mechanism, or manually. They are thenindividually heated in the injection cannula 140. In one embodiment,they are stacked in a linear or circular array. Alternately, they couldbe transferred individually into the injection cannula by the userwithout the aid of an internal mechanism or cartridge.

In one embodiment, one or more heating elements are provided at a tipregion 150 surrounding the injection cannula 140. The heating elementsin the tip region provide further control of the polymer temperature asit comes into contact with tissue and forms a fastener.

In one embodiment the injection cannula 140 is actively heated in theentire region from the first end 142 to the second end 144. In oneembodiment at least part of the heat for the injection cannula isgenerated through an actively regulated heater in order to maintainconsistent temperatures. Once the cannula exits the distal tip, it isexposed to variable thermal conditions (i.e. dry bone, wet bone, roomtemperature, physiological temperature). Active temperature regulationwill help to maintain a consistent temperature profile in the cannula.In one embodiment, a thermal gradient is provided in the injectioncannula 140 where the polymer 122 is at a higher temperature in aproximal region 154 of the tip than at a distal end 152 of the tip 150.The higher temperature at the proximal end 154 facilitates improved flowcharacteristics, while the lower and more tightly controlled temperatureat the distal end 152 reduces the possibility of necrosis in tissue. Inone embodiment, multiple heating elements and/or thermal controlcircuits are used to control the temperature gradient.

FIG. 2 shows a close of view of the tip 150 of the bone supportattachment device 100 during formation of a fastener. A cross sectionview of a bone support structure 210 is shown located adjacent to aportion of bone 212. A hole 218 is included through the bone supportstructure 210 and a corresponding hole 220 is included in the bone 212.

In one embodiment, the bone support structure 210 includes a plate,although other forms of support structures are within the scope of theinvention. In one embodiment, the bone support structure 210 is formedfrom a bioresorbable material such as a bioresorbable polymer. In oneexample, the bone 212 is a thin layer of bone, such as a portion of askull, although the invention is not so limited. An interface 214 isformed between the bone support structure 210 and the bone 212. As shownin the Figure, frequently a gap is included at the interface 214.

In one embodiment, a depth gauge 112 is included near the tip 150 of thebone support attachment device 100. An example of a depth gauge includesa static shelf that butts against the bone support structure 210 andlimits a depth that the injection cannula 140 travels within the holes218 and 220. The depth gauge 112 determines where in the holes 218 and220 the second end 144 of the injection cannula 140 is located. In oneembodiment, the desired depth of the second end 144 is through the hole218 in the bone support structure 210, past the interface 214 andpartially into the hole 220 in the bone. By passing the interface withthe second end 144, a possibility of polymer being extruded into a gapat the interface 214 is reduced or eliminated.

Extrusion of polymer between any gap at the interface is undesirable fora number of reasons. Any polymer that is accidentally extruded at theinterface is not available to form structural portions of the fastener,therefore strength of the fastener is lessened by extrusion into a gapat the interface. Further, any extrusion at the interface tends to openany existing gap further.

In one embodiment, the depth gauge 112 is dynamic. For example, in oneembodiment, once a predetermined volume of polymer is extruded into theholes 218, 220, the depth gauge is moved to retract the second end 144of the injection cannula 140 from the holes 218, 220.

In selected embodiments, the position of the depth gauge 112 is userselectable to adapt to plates of various thicknesses and holes ofdifferent depths. In one embodiment the depth gauge 112 is larger thanthe hole 218 or any countersunk area around the hole 218 in the bonesupport structure 210. This allows the surgeon to compress the bonesupport structure 210 against the tip 150 against the bone 212. In analternate embodiment the depth gauge 112 is slideably attached, and thesecond end 144 of the cannula 140 protrudes only when the instrument iscompressed against the bone support structure 210. This feature wouldprotect the second end 144 except when injection is about to take place.In one embodiment the second end 144 of the cannula 140 seals against aportion of the tip 150 so as to not allow extraneous fluid and matter toenter the inside of the injection cannula 140 or between the cannula andtip 150.

In one embodiment, the outer diameter of the second end 144 of thecannula 140 is slightly smaller than the hole 220 in the bone 212.Without implying limitation, this diameter would generally fall withinthe range of 1.3 to 3.5 mm at the most distal point. This is to allowthe cannula 140 to enter the hole 220 in the bone 212 with minorresistance. In one embodiment, the hole 220 in the bone 212 is taperedor stepped to allow for a larger opening for entry of the cannula 140and a smaller hole to minimize the amount of material required to fillthe entire opening.

FIG. 2 further shows a volume of expelled polymer 160. The process ofexpelling a polymer in contrast to heating in place has an advantage offorming a cooled profile across the volume of expelled polymer 160. Asurface 162 of the expelled polymer cools first on contact with tissueor other external surfaces. The interior of the expelled polymer remainsflowable, and tends to form a desirable shape similar to blowing up aballoon. The balloon shape helps to form a mechanical bond in the bone212 similar to a rivet. Additionally, the cooled surface 162 is far lesslikely to cause thermal necrosis with tissue it comes into contact with.In contrast, for example, polymer that is heated through sonic vibrationin a hole in bone is hottest at the interface between the bone and thepolymer.

In one embodiment, the plunger 130 has a slight clearance fit relativeto the inner walls of the injection cannula 140. The clearance isgenerally within the range of 2 to 200 μm. The clearance should be smallenough as to not allow polymer to flow past the distal tip of theplunger yet large enough as to not create mechanical interference. Inone embodiment the plunger 130 rotates as it translates to createadditional friction as it travel within the cannula 140. This frictionproduces heat which reduces the viscosity of any polymer which flowsbetween the cannula 140 and plunger 130. This rotation can be achievedthrough the attachment of the plunger 130 to the rotating lead screw108. In one embodiment the clearance is eliminated at the second end 144of the cannula 140 and an interference fit is achieved. An interferencefit helps to sever any polymer from the plunger 130 and cannula 140 atthe end of the cycle.

In one embodiment, the entire plunger 130 or at least the distal end ofthe plunger 130 is manufactured from or coated with a non stick materialsuch as silicone or PTFE. This prevents polymer from adhering to theplunger 130 after a formed fastener is completed.

As discussed above, in one embodiment, the temperature profile ofinjection cannula 140 is controlled to allow the polymer to remainsufficiently flowable yet not induce thermal necrosis into the bone atthe second end 144. Thermal necrosis in living tissue is a complex timeand temperature dependent relationship, but is often considered to beginwhen the tissue reaches 48° C. Additionally, the bone support device 210or plate may begin to deform under thermal stress. If, for example, apolylactide/polyglycolide polymer is used, a suitable range around aglass transition temperature of 48-55° C. is used for the injectioncannula 140.

The rate at which the polymer cools within the cannula is dependent uponthe rate at which it travels. Thus a lower temperature of the cannula atthe distal end could be permitted if the polymer travels at a highenough rate such that it does not have sufficient time to equilibratewith the temperature of cannula itself.

In one embodiment the tip 150 of the bone support attachment device 100acts as a heat sink and dissipates the heat from distal portion of thecannula 140 allowing for reduced temperature. This dissipating effectcan be optimized through the use of thermally conductive materials anddesigns to accentuate heat transfer through conduction and convection.Such materials include, but are not limited to, aluminum, aluminumfilled polymers, copper, brass, conductive metal, silver, and thermallyconductive polymers or ceramics. Designs to promote heat transferinclude, but are not limited to fins, vanes, ribs, pins, and spikes,etc. Active cooling could also be incorporated including, but notlimited to, syringe irrigation, gases (N₂, air or CO₂), liquid nitrogen,peltier effect devices, vortex chillers, pumped saline, fans andrecirculating chilled liquids. These methods of cooling the second end144 of the cannula 140 can also be used to cool the polymer head once ithas been formed as disclosed below.

As the polymer exits the second end 144 of the cannula 140 and into thebone 212, it begins to flow and interdigitate into any pores within thebone 212. FIG. 3 illustrates the flow anticipated when a hole 308 is inrelatively non porous material and the hole extends through the bone304. In this case, the polymer expands on the far cortex and forms abulbous tip 312 with a diameter larger than the hole created 308. Thisprovides for a rivet-like effect with additional pullout resistance.

FIG. 3 further illustrates a strengthening property that is unique to anextrusion process as described in the present disclosure. Duringextrusion, through a plate 300 and into bone 320, polymer molecules 320are stretched and aligned along a long axis of the fastener 310. Thealignment of the polymer molecules provides significant increases infastener strength. In selected embodiments, strength of the fastener isincreased by up to at least 75% over non-extruded polymer. A number ofprocess variables such as the temperature at or around the glasstransition temperature during extrusion contribute to alignment ofpolymer molecules.

FIG. 4 illustrates the flow anticipated when a fastener 410 is injectedinto porous or cancellous bone 404. In this case the polymer can flowinto the interstices 412 of the bone 404 and interdigitate with it. Thisalso provides pullout resistance. The embodiment shown in FIG. 4 alsoillustrates alignment of molecules 420 and strengthening of the fastener410.

Referring again to FIG. 3, the head 314 that is formed by the fasteneris allowed to substantially fill a countersink recess 302 in the plate300. This provides locking of the fastener 310 to the plate 300 yetallows rotational motion. If locking in rotation is also desired, thecountersunk recess can be incorporate grooves or other surfaceirregularities that the polymer can flow into. The injected polymer andfixation device can also be bonded together if melted.

FIG. 5 illustrates an example of a bone plate 500. As discussed above,bone plates 500 are included in the category of bone support structure,however additional bone support structures other than plates areincluded within the scope of the invention. Holes 504 are shown toaccept polymer fasteners as described in embodiments above. Other plateportions 502 form structure between the holes 504.

FIG. 6 illustrates one example use of bone plates in conjunction withpolymer fasteners as described in embodiments above. A skull 600 is usedas an example portion of bone. A first plate 604 is shown secured to theskull 600 using a number of bone plates 602 and polymer fasteners asdescribed in selected embodiments above.

FIG. 7 illustrates an example method according to an embodiment of theinvention. An amount of polymer is heated heating to a temperature at orabove its glass transition temperature. A hole is drilled in a bone toaccept a fastener. The hole in the bone is aligned with a hole in asupport structure, such as a bone plate. A cannula is inserted throughthe hole in the support structure, past an interface between the supportstructure and the bone, and at least partially into the hole in thebone. As discussed above, the insertion of the cannula to this locationhelps prevent extrusion of polymer at the interface. Insertion of thecannula further aids in alignment of the holes. The heated amount ofpolymer is then expelled from a tip of a cannula, into the hole in thebone, and the cannula is removed from the hole in the bone and the holein the support structure. The polymer left in the holes forms afastener, as described in selected embodiments above.

While a number of example embodiments and advantages of the inventionare described, the above examples are not exhaustive, and are forillustration only. Although specific embodiments have been illustratedand described herein, it will be appreciated by those of ordinary skillin the art that any arrangement or method which is calculated to achievethe same purpose may be substituted for the specific embodiment shown.This application is intended to cover any adaptations or variations ofthe present invention. It is to be understood that the above descriptionis intended to be illustrative, and not restrictive. Combinations of theabove embodiments, and other embodiments will be apparent to those ofskill in the art upon reviewing the above description. The scope of theinvention includes any other applications in which the above structuresand methods are used. The scope of the invention should be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow thereader to quickly ascertain the nature and gist of the technicaldisclosure. The

Abstract is submitted with the understanding that it will not be used tointerpret or limit the scope or meaning of the claims.

1. A bone support attachment device, comprising: an injection cannulasized to hold an amount of polymer to form a single fastener; a polymersupply inlet coupled to a side of the injection cannula; a plungerhaving a tip disposed at a first end of the injection cannula such thatwhen actuated, the plunger cuts off the supply inlet and subsequentlyexpels the amount of polymer from a second end of the injection cannulaupon the plunger reaching the second end of the injection cannula; achamber sized to house a block of polymer sufficient to form a pluralityof fasteners, the chamber connected to the supply inlet to sequentiallyprovide the amount of polymer to form a single fastener from a singlechamber full of polymer; and an actively regulated heater configured tomaintain a consistent temperature profile from the first end of thecannula to the second end of the cannula,wherein the temperature profilecomprises a temperature gradient from the first end of the injectioncannula to the second end of the injection cannula and wherein thetemperature gradient is warmer at the first end of the injection cannulathan at the second end of the injection cannula.
 2. The bone supportattachment device of claim 1, wherein a starting plunger location isvariable to provide a variable volume in the injection cannula thatcorresponds to a selectable amount of polymer to form fasteners ofvarious sizes.
 3. The bone support attachment device of claim 1, whereina temperature at the second end of the injection cannula is controlledin a range within approximately 37-55 degrees Centigrade.
 4. The bonesupport attachment device of claim 1, further comprising a chamberplunger configured to expel polymer from the chamber into the injectioncannula when actuated.
 5. The bone support attachment device of claim 1,wherein the chamber is configured to receive a plurality of discretepolymer sections that are not heated in the chamber.
 6. The bone supportattachment device of claim 1, wherein at least a portion of the plungeris configured to reduce adhesion of polymer to the plunger.
 7. The bonesupport attachment device of claim1, further comprising an actuatorconfigured to advance the plunger at a rate sufficient for at least aportion of the polymer expelled from the cannula to interdigitate withina bone into which the injection cannula is extended.
 8. The bone supportattachment device of claim 1, further comprising an actuator configuredto advance the plunger at a rate sufficient to form a bulbous polymertip proximate a point distal to the second end of the injection cannula,the point distal to the second end of the injection cannula beingdefined by an inner cortical bone surface that is opposite a corticalbone surface upon which a bone support is positioned when the injectioncannula is extended through the bone support during operation of thebone support attachment device.
 9. The bone support attachment device ofclaim 1 wherein the actively regulated heater comprises multiple heatingelements.
 10. The bone support attachment device of claim 1 wherein theactively regulated heater comprises multiple thermal control circuits.11. The bone support attachment device of claim 1 further comprising adepth gauge proximate a distal tip of the bone support attachmentdevice, the depth gauge configured to move relative to the injectioncannula once a predetermined volume of polymer is expelled from theinjection cannula.
 12. The bone support attachment device of claim 11,wherein the second end of the injection cannula is configured to extenda selectable distance from the depth gauge, the selectable distancebeing greater than a thickness of a bone support such that when the bonesupport is engaged with a static shelf of the depth gauge, the secondend of the injection cannula extends completely through the bonesupport.
 13. The bone support attachment device of claim 11, wherein thedepth gauge is positionable at a selectable distance from the distaltip.
 14. The bone support attachment device of claim 1 wherein theactively regulated heater is configured to raise the temperature ofpolymer within the injection cannula to the melting point of the polymerand is configured to actively control the temperature of polymer at thesecond end of the injection cannula to a temperature that is low enoughto not cause necrosis when the polymer is discharged from the injectioncannula to contact tissue.
 15. The bone support attachment device ofclaim 1 wherein the actively regulated heater is configured to raise thetemperature of polymer within the injection cannula to between 50° C.and 250° C.
 16. The bone support attachment device of claim 15 whereinthe actively regulated heater is configured to raise the temperature ofpolymer within the injection cannula to between 130° C. and 180° C.